1. Field of the Invention
Aspects of the present invention relate to a quality of service (QoS) securing apparatus and method using a communication protocol and, more particularly, to a method and apparatus for securing QoS of data communication by exchanging information using a communication protocol between a reception side and a transmission side.
2. Description of the Related Art
Owing to the development of wired/wireless communication technology, wired/wireless communication services supporting multimedia come in a variety of types and standards. In particular, with increased data transmission speeds, more services provide music or movies in real-time streaming through wired/wireless communication. In this regard, it is very important to allow service users to listen to music or to see movies seamlessly. A method of securing quality of service (QoS) for ensuring seamless data communication between a reception side and a transmission side is critical to a communication environment as described below.
FIG. 1 is a diagram of a conventional data communication session showing a handover between heterogeneous networks. Referring to FIG. 1, a mobile terminal of a reception side 110 moves from a wireless LAN network 130 having a maximum data transmission speed of 2 Mbps to a Wideband Code Division Multiple Access (WCDMA) network 140 having a maximum data transmission speed of 384 Kbps. A transmission side 120 transmits data at a speed of 1 Mbps (101) in the wireless LAN network 130 having a maximum data transmission speed of 2 Mbps before the mobile terminal of the reception side 110 performs the handover (102). Even after the handover (102) is performed, since the transmission side 120 is not informed of link characteristics of the WCDMA network 140 to which the mobile terminal of the reception side 110 moved, the transmission side 120 continues to transmit data (103) at the same speed of 1 Mbps. As a result, the mobile terminal of the reception side 110 cannot entirely receive the data transmitted from the transmission side 120, resulting in data loss. Therefore, if the transmission side 120 transmits streaming data of music or movie, the reception side 110 cannot seamlessly listen to music or see movies in real time.
FIG. 2 is a diagram of another conventional data communication session according to a handover between heterogeneous networks. Referring to FIG. 2, contrary to the data communication session illustrated in FIG. 1, a mobile terminal of a reception side 210 moves from a WCDMA network 230 having a maximum data transmission speed of 384 Kbps to a wireless LAN network 240 having a maximum data transmission speed of 2 Mbps. A transmission side 220 transmits data at a speed of 384 Kbps (201) before the mobile terminal of the reception side 210 performs the handover (202). Even after the handover (202) is performed, since the transmission side 220 is not informed of the link characteristics of the wireless LAN network 240 to which the mobile terminal of the reception side 210 moved, the transmission side 220 continues to transmit data (203) at the same speed of 384 Kbps. As a result, the transmission side 220 transmits the data at the inefficient speed of 156 Kbps in the wireless LAN network 240, which has a maximum data transmission speed of 2 Mbps.
Like the handover between heterogeneous networks, illustrated in FIGS. 1 and 2, network link characteristics after a handover between homogeneous networks is performed can be different from those before the handover is performed. If a network has more users after the handover is performed than that before the handover is performed, users communicate with each other at a slow speed in the network. Also, if the network has a higher bit error rate after the handover is performed than before the handover is performed, data is transmitted at a lower speed in order to reduce the bit error rate. If the network has fewer users and a lower bit error rate after the handover is performed than that before the handover is performed, data is transmitted at a higher speed.
When a reception side communicates in a network without a handover between networks, data transmission speed may vary due to changes in the number of users in the network and a data communication environment.
Information about a change in usable resources necessary for processing data being received by a terminal of a reception side can influence the QoS of data communication. Although the terminal of the reception side cannot process the data currently being received due to a change of hardware characteristics of a CPU, memory, etc., which are used to process the data, if a transmission side transmits data, the terminal of the reception side cannot properly receive the data. If the transmission side transmits encoded music or movie that cannot be processed by the reception side, the terminal of the reception side cannot properly receive the music or movie.
The transmission side transmits data according to a changed communication environment, so that the QoS of data transmission can be secured. For example, data of a lower quality music or movie can be transmitted in a network having a lower transmission speed than in another network, in order to provide a real time service. Also, data of a higher quality music or movie can be transmitted in a network having a faster transmission speed than in another network, in order to provide a good quality streaming service. If more of the CPU or memory is allocated to the reception side in order to process data transmitted from the transmission side, the transmission side can transmit data of a higher quality music or picture than before the CPU or memory is allocated.
Conventional sliding window congestion control using the TCP protocol is used to change the size of data according to the communication environment of the reception side. The reception side transmits an acknowledgment (ACK) signal indicating that the reception side has received data from the transmission side without an error. The transmission side receives the ACK signal normally and increases the amount of data transmitted at a time. However, if the transmission side does not receive the ACK signal, the transmission side reduces the amount of data transmitted at a time. Since data transmission speed can be controlled according to improvement or deterioration of the link characteristics of the reception side, the transmission side can transmit data based on the link characteristics of the reception side. However, conventional sliding window congestion control requires considerable time to transmit data based on the improved or deteriorated link characteristics of the reception side, which causes links to be ineffectively used during the delayed time.